Blow molding machines conventionally provide a tube of hot plastic between open sections of a mold. Closing of the mold then clamps the hot plastic tube and allows air to be blown into the tube such that it assumes the shape of the mold. After suitable cooling has taken place, the mold sections are opened to allow ejection of the molded part.
Blow molded parts such as containers have conventionally included paper labels that are glued thereto after the molding to identify the contents of the container to the consumer. One problem is that such paper labels can become wrinkled if dampened and can also become detached from the container if a waterproof glue is not used. Also, paper labels require a separate labeling step after the molding which thus adds to the cost of the container.
In-mold labeling has been developed in the recent past to provide superior bonding of labels to blow molded plastic parts. This in-mold labeling is performed by initially inserting a label within the mold prior to the introduction of the hot plastic tube and by subsequently closing sections of the mold in preparation for the blowing operation. The subsequent blowing operation forms the hot plastic tube around the label to the shape of the mold and activates a heat sensitive adhesive that provides a permanent bond which is incapable of being broken by moisture or otherwise. Also, such in-mold labeling provides smooth transition between the label and the adjacent surface of the molded plastic part and further provides additional strength since the label cooperates with the plastic in resisting deformation. Such strengthening also allows the use of less plastic to blow mold the part and thereby reduces the ultimate cost to the consumer. Furthermore, when utilized with containers for carbonated beverages, it is believed that in-mold labeling may reduce the flow of carbon dioxide out through the container wall over a period of time and thereby increases the shelf life.
Prior in-mold label dispensers for blow molding machines conventionally include a label carrier having vacuum cups that receive a label from a label magazine and then are movable to deposit the label within the mold cavity whereupon termination of a vacuum drawn at the suction cups allows a vacuum drawn at the mold cavity to secure the label in position in preparation for the molding. Such vacuum carriers have previously been mounted on linkages that move the labels in an angular path with respect to the direction of opening and closing movement of mold sections of the mold in order to permit depositing of the labels in the confined space permitted by the extent of the mold opening. With the linkage type of label carrier, only one label can be deposited within the mold at a given time since movement thereof on the linkage toward one mold section interfers with movement of a similar linkage toward an opposed mold section for depositing another label.
Another prior art type of in-mold label dispenser is disclosed by U.S. Pat. No. 4,359,314 and includes a label carrier that is moved along an abruptly curved path by a complex linkage which executes a 180 degree turn in order to transfer labels from a label magazine to the mold in preparation for molding. With this complex linkage type label dispenser, it is likewise not possible to deposit more than one label in the mold at a given time due to the limited space present upon opening of the mold.
With both of the above prior art type of in-mold label dispensers, the cycle time of the blow molding machine is increased due to the necessity of depositing labels sequentially rather than at the same time when more than one label is to be applied to each mold.
U.S. Pat. Nos. 3,292,209 and 4,397,625 each disclose an in-mold label dispenser wherein fluid motors are utilized to both: (1) move a label dispensing head to between open mold sections of a mold; and (2) extend label carriers to deposit the labels on the mold sections prior to retracting the label carriers and thereafter withdrawing the dispensing head in preparation for mold closing and blowing of the plastic article within the mold. With such dispensers, the use of fluid motors makes it difficult to accurately position the labels within the mold due to the tolerances involved with the dispensing head and label carrier movements.
U.S. Pat. No. 3,324,508 discloses an in-mold label dispenser wherein a linkage moves labels from rolls of labels to a mold where the labels are held by an electrostatic charge prior to the blow molding operation.
U.S. Pat. Nos. 4,479,770 and 4,479,771 of William A. Slat, et al disclose in-mold label dispensers wherein a first solid mechanical drive moves a dispensing head between inserted and withdrawn positions with respect to an open mold and wherein a second solid mechanical drive extends and retracts label carriers in order to perform the labeling operation. Use of such solid mechanical drives to move the dispensing head and the label carriers permits accurate positioning of the labels. The ability to accurately position the labels is extremely important, especially when utilized with a plastic blow molding machine of the rotary wheel type wherein the molds are mounted for opening and closing movement on a wheel that rotates. The speed at which the wheel rotates is sufficiently fast to require close tolerances in the label timing and positioning.